GEC for Conex Container

[brother]

Seen a job recently where they turned a basic shipping Conex (all metal) Container into a small tool shed/workshop. It is not attached to anything else, a stand alone. They ran 2 , 120 volt circuits to it. They did pull an equipment ground to it. My question is per code, are they required to have a GEC, (grounding electrode conductor) ? It appears they would need to drive 2 ground rods to accomplish this.

 

[infinity]

If they used a MWBC for the two circuits then no GES is required. Two separate 120 volt circuits each with its own neutral is technically a violation.

 

[brother]

If they used a MWBC for the two circuits then no GES is required. Two separate 120 volt circuits each with its own neutral is technically a violation.

Thanks for info. Do you know why they made an exception for the MWBC? if it was lighting they were concerned about in the NEC then what difference would the mwbc make vs a 2 circuit with its own neutral?

 

[ptonsparky]

A MWBC is one circuit, it happens to have a neutral.

 

[ActionDave]

My guess would be they made the exception allowing a MWBC to go to a separate structure because it's a miniature feeder.

 

[brother]

A MWBC is one circuit, it happens to have a neutral.

I guess i was not clear enough in my last post. I know the mwbc has a neutral, I was referring to the 2 circuits with their 'own' seperate neutral.

 

[ActionDave]

I guess i was not clear enough in my last post. I know the mwbc has a neutral, I was referring to the 2 circuits with their 'own' seperate neutral.

That's never been allowed.

 

[brother]

That's never been allowed.

What has never been allowed?

 

[ActionDave]

Two separate circuits to a separate structure.

 

[brother]

Two separate circuits to a separate structure.

Thanks. It appeared it was implied it was ok to have 2 circuits in Article 250. Do you know what NEC article forbids this?

 

[kwired]

Thanks. It appeared it was implied it was ok to have 2 circuits in Article 250. Do you know what NEC article forbids this?

A MWBC is considered 1 branch circuit. With 120/208 supply you could have the equivalent capacity of 3 120 volt branch circuits in one MWBC, or if you had some kind of hexaphase system even more equivalent individual circuits in one MWBC.

Yet in art 210 you can have one 3 wire MWBC serve the required 2 SABC's in a dwelling.

confused yet?

 

[ActionDave]

Thanks. It appeared it was implied it was ok to have 2 circuits in Article 250. Do you know what NEC article forbids this?

225.30

 

[infinity]

A MWBC can be considered one circuit when supplying a separate structure. It is not always considered one circuit. This is for a separate structure:

Part II. Buildings or Other Structures Supplied by a Feeder(s)
or Branch Circuit(s)
225.30 Number of Supplies. A building or other structure
that is served by a branch circuit or feeder on the load side of a
service disconnecting means shall be supplied by only one
feeder or branch circuit unless permitted in 225.30(A)
through (E). For the purpose of this section, a multiwire
branch circuit shall be considered a single circuit

 

[brother]

My guess would be they made the exception allowing a MWBC to go to a separate structure because it's a miniature feeder.

Thanks for all the clarity everyone. But im still curious as from a real world practical safety standpoint. If the GEC is for lightning protection, how are these restrrictions on other circuits making it safer for lighting??

 

[kwired]

Thanks for all the clarity everyone. But im still curious as from a real world practical safety standpoint. If the GEC is for lightning protection, how are these restrrictions on other circuits making it safer for lighting??

GES is not a lightning protection system. It does give a ground reference that can help with transients from lightning as well as transients from the POCO system that can come from switching or even incidental contact at times with higher voltage systems.

NEC maybe puts a little more emphasis than is really needed on grounding electrode systems, and some inspectors seem to be "dirt worshipers" at times and act like this is the most critical thing of the entire installation. Reality is with a direct lightning strike it will do very little to protect you from having some significant damages. Surge from indirect strike - it is all going to depend on conditions as to how much damage you may see.

The utility grid already has an electrode at nearly every structure and usually connected to a grounded conductor between those structures making it a very low impedance overall and one less electrode at your building isn't going to make that much difference to the entire system, it just gives your building an additional reference at the building.